Mechanisms Controlling the Energy Barrier for Ion Hopping in Polymer Electrolytes

Abstract

The present work studies the mechanisms controlling the energy barrier for ion hopping in conducting polymers. Polymer electrolytes usually show Arrhenius-like temperature dependence of the conductivity relaxation time (characteristic time of local ion rearrangements) at temperatures below their glass transition T g . However, our analysis reveals that the Arrhenius fit of this regime leads to unphysically small prefactors, τ 0 ≪ 10 −13 s. Imposing a value of 10 −13 s for this parameter renders the fairly unexpected result that the energy barrier for charge transport in these polymers has strong temperature dependence even below T g . Our study also reveals significant temperature variations of the dielectric permittivity and the instantaneous shear modulus in the glassy state of these polymers. Using the Anderson and Stuart model, we demonstrate that these variations provide strong justifications for the temperature variation of energy barrier for ion hopping. Most importantly, the proposed approach reveals that the energy barrier controlling ion hopping in polymer electrolytes is significantly (∼30−40%) lower than that estimated using traditional Arrhenius fit. These new insights call for revisions of many earlier results based on apparent Arrhenius fits, and the newly proposed approach can provide more accurate guidance for the design of solid-state electrolytes with enhanced ionic conductivity.

Relaxation and diffusion of an ionic plasticizer in amorphous poly(vinylpyrrolidone)

“…15–19 In fact, for instance in the field of polymer electrolytes and other ion conducting systems decoupling of charge and structure dynamics is highly desired. 20–23…”

“…Another area of research, which is particularly relevant for energy storage technologies, is the transport of penetrants that act as electric charge carriers in polymer matrices. 23,53–55 The workhorse material here is polyethylene oxide, 56 a semicrystalline polar polymer doped with various salts in a rather reduced concentration range. 57 While the resulting polymer electrolytes mitigate several drawbacks of inorganic conductors by providing mechanical flexibility and good contact with the electrodes, they often suffer from reduced electrochemical stability.…”

Conductivity and Transference Numbers in Lithium Salt-Doped Block Copolymeric Ionic Liquid Electrolytes

“…Ion transport mechanisms in homopolymeric PolyILs have been the subject of a number of experimental ,− and computational investigations. − In contrast to polymer segmental dynamics assisted ion transport in neutral polymer electrolytes, it has been demonstrated that ion transport in PolyILs involves a series of association/dissociation events involving multiple polycations from distinct polymer chains . A number of more recent studies have also clarified the influence of counterion identity, ,,, molecular weight, , polymer architecture, and so on − on the ion transport mechanisms in PolyILs …”

Nanostructured Single-ion Polymer Blend Electrolytes Composed of Polyanionic Particles and Low Molecular Weight PEO

“…several orders of magnitude below the required value for applications. This is the result of the high glass transition temperature, T g , of polyanions that limits Li + mobility . As an example, the T g of the widely studied lithium poly­[(4-styrenesulfonyl)­(trifluoromethane-sulfonyl)­amide (LiPSTFSI) polyanion has been reported to be in the range of 210 to 260 °C for molecular weights ranging from 2.5 to 160 kDa. − , To increase ion conductivity at RT, the polyanion chains are often blended with a low T g polar polymer host, typically poly­(ethylene oxide) (PEO).…”

“…Anionic polyelectrolytes, termed as single-ion polymer electrolytes (SI-PEs), have been studied and developed to alleviate these issues; ,,, the anion is covalently linked to the polymer backbone and only the cation is free to move resulting to a transference number close to unity. Among the various polyanionic systems that have been developed, the ones that contain (trifluoromethanesulfonyl) imide (TFSI – ) has attracted the majority of research attention due to their highly delocalized negative charge over large conjugated structure. − Despite the considerable research efforts in single-ion electrolytes, the realization of their potential has been hampered by the incapacity to design materials that have simultaneously high enough, for practical applications, ionic conductivity, and good mechanical properties.…”